We are likely to just consider viruses when it comes to their damaging impacts on human health and lives. The 1918 flu pandemic killed around 50 million people. Smallpox claimed 30% of those that caught it, and survivors were often scarred and blinded. More recently, we’re all too acquainted with the health and economic impacts of COVID.
But viruses may also be used to profit human health, agriculture and the environment.
Viruses are comparatively easy in structureconsisting of a bit of genetic material (RNA or DNA) enclosed in a protein coat (the capsid). Some even have an outer envelope.
Viruses get into your cells and use your cell machinery to repeat themselves.
Here are six ways we’ve harnessed this for health care and pest control.
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1. To correct genes
Viruses are utilized in some gene therapies to correct malfunctioning genes. Genes are DNA sequences that code for a selected protein required for cell function.
If we remove viral genetic material from the capsid (protein coat) we are able to use the space to move a “cargo” into cells. These modified viruses are called “viral vectors”.
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Viral vectors can deliver a functional gene into someone with a genetic disorder whose own gene is just not working properly.
Some genetic diseases treated this manner include haemophilia, sickle cell disease and beta thalassaemia.
2. Treat cancer
Viral vectors might be used to treat cancer.
Healthy people have p53, a tumour-suppressor gene. About half of cancers are related to the lack of p53.
Replacing the damaged p53 gene using a viral vector stops the cancerous cell from replicating and tells it to suicide (apoptosis).
Viral vectors may also be used to deliver an inactive drug to a tumour, where it’s then activated to kill the tumour cell.
This targeted therapy reduces the negative effects otherwise seen with cytotoxic (cell-killing) drugs.
We can even use oncolytic (cancer cell-destroying) viruses to treat some forms of cancer.
Tumour cells have often lost their antiviral defences. In the case of melanomaa modified herpes simplex virus can kill rapidly dividing melanoma cells while largely leaving non-tumour cells alone.
3. Create immune responses
Viral vectors can create a protective immune response to a selected viral antigen.
One COVID vaccine uses a modified chimp adenovirus (adenoviruses cause the common cold in humans) to move RNA coding for the SARS-CoV-2 spike protein into human cells.
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The RNA is then used to make spike protein copies, which stimulate our immune cells to duplicate and “remember” the spike protein.
Then, when you’re exposed to SARS-CoV-2 for real, your immune system can churn out a number of antibodies and virus-killing cells in a short time to forestall or reduce the severity of infection.
4. Act as vaccines
Viruses might be modified to act directly as vaccines themselves in several ways.
We can weaken a virus (for an attenuated virus vaccine) so it doesn’t cause infection in a healthy host but can still replicate to stimulate the immune response. The chickenpox vaccine works like this.
The Salk vaccine for polio uses an entire virus that has been inactivated (so it may well’t cause disease).
Others use a small a part of the virus resembling a capsid protein to stimulate an immune response (subunit vaccines).
An mRNA vaccine packages up viral RNA for a particular protein that may stimulate an immune response.
5. Kill bacteria
Viruses can – in limited situations in Australia – be used to treat antibiotic-resistant bacterial infections.
Bacteriophages are viruses that kill bacteria. Each kind of phage often infects a selected species of bacteria.
Unlike antibiotics – which regularly kill “good” bacteria together with the disease-causing ones – phage therapy leaves your normal flora (useful microbes) intact.
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6. Target plant, fungal or animal pests
Viruses might be species-specific (infecting one species only) and even cell-specific (infecting one kind of cell only).
This occurs since the proteins viruses use to connect to cells have a shape that binds to a particular kind of cell receptor or molecule, like a particular key matches a lock.
The virus can enter the cells of all species with this receptor/molecule. For example, rabies virus can infect all mammals because we share the suitable receptor, and mammals produce other characteristics that allow infection to occur whereas other non-mammal species don’t.
When the receptor is just found on one cell type, then the virus will infect that cell type, which can only be present in one or a limited variety of species. Hepatitis B virus successfully infects liver cells primarily in humans and chimps.
We can use that property of specificity to focus on invasive plant species (reducing the necessity for chemical herbicides) and pest insects (reducing the necessity for chemical insecticides). Baculovirusesfor instance, are used to regulate caterpillars.
Similarly, bacteriophages might be used to regulate bacterial tomato and grapevine diseases.
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‘Phage therapy’ could treat some drug-resistant superbug infections, but comes with unique challenges
Other viruses reduce plant damage from fungal pests.
Myxoma virus and calicivirus reduce rabbit populations and their environmental impacts and improve agricultural production.
Just like humans might be protected against by vaccination, plants might be “immunised” against a disease-causing virus by being exposed to a milder version.